According to a conventional technique, a plurality of ring oscillators each including an odd number of inverters are connected in a loop to form a loop-type multi-phase oscillator. One node in each ring oscillator is connected to a corresponding node in the ring oscillator of the next stage via inverters for phase coupling (see Patent Document 1).
According to another conventional technique, a plurality of ring oscillators, each including an odd number of inverters, are connected in an array to form an array-type multi-phase oscillator with high phase resolution. Each of a plurality of nodes in each ring oscillator is connected to a corresponding node in the adjacent ring oscillator via an inverter for phase coupling (see Patent Document 2).
Patent Document 1: Specification of U.S. Pat. No. 5,592,126
Patent Document 2: Specification of U.S. Pat. No. 5,475,344